Burner control system



1945. J. J. ROTHWELL ETAL 2,367,059

BURNER CONTROL SYSTEM Filed Feb. 10, 1941 Patented Jan. 9, 1945 BURNER CONTROL SYSTEM;

John J. Riothwell, Elkhart, and Leland B. Wagner, Goshen, Ind., assigners to Penn Electric Switch 00., Goshen, Ind., a corporation of Iowa Application February 10, 1941, Serial No. swam 6 Claims as to de-energize the circuit as a. result of combustion failure initially, combustion failure after establishment, or failure of a safety heater, such as a burnt-out condition thereof.

, Another object is to provide a combustion switch'which is extremely simple in construction and inexpensive to manufacture and which may be arranged to respond to combustion by exposing a certain bimetal element of the combustion switch to heat radiated from the, combustion chamber, it being unnecessary to locate the thermostat inside'a stack or the like nor inside the combustion chamber, but merely externally of the chamber with an opening through the wall of the chamber to expose the bimetal element to the. heat therein.

A further object is to provide a modified form of combustion switch in our burner control system which looks out instead of recycling after a flame failure occurs.

Still a further object is to provide a burner control system including a combustion switch which may be connected in either low voltage control circuits or high voltage main circuits of diii'erent burner systems and which will operate in its intended manner under the influence of a wide variation of conditions.

With these and other objects in view, our system consists in the construction, arrangement and combination of the various parts thereof whereby the objects contemplated are attained, as hereinafter more fully set forth,.pointed out in our claims and illustrated in the accompanying drawing. Although our system is susceptible.- of

a variety of embodiments, it is unnecessary to fully described and illustrate more than a few in order to give a full understanding of the system both from structural and functional standpoints.

Accordingly, we have illustrated a preferred and voltage room thermostat or control circuit, the

combustion switch being shown in cold position;

Figures 2, 3 and 4 show respectively the combustion switch in hot, initial combustion failure. and combustion failure after established, positions;

anism. wi

burner.

Figure 5 is a diagrammatic view of a portion of Figure'l showing a slight modification;

Figure 8 is a diagrammatic view showing our system applied to an all high voltage circuit; and

Figure 7 is a view similar to Figure 3 showing a modified construction.

On the accompanying drawing, we have used the reference character BM to indicate a burner motor, and Ian the ignition mechanism for the A motor switch MS controls energize.- tion of the urner motor-and the ignition mecheurrent being supplied through line wires- "and 20. The wires I! and II also extend to the primary P of a transformer T.

A room thermostat RT is illustrated and a low voltage circuit therefor is-energized from the secondary S of the transformer '1'. The secondary circuit includes a relay coil RC and a safety heater H, together with combustion switchcontacts II and II.

The combustion switch for the contacts II and ll is indicated generally at CS and includes a pair of bimetal elements It and I2 anchored as to a support It oi insulating material. The contacts it and I! are carried by the bimetal elements It and I2, respectively. The bimetal element It carries a support it for a permanent magnet I! which is adapted to cooperate, for a purpose which will hereinafter appear, with an armature it. The armature I8 is carried by the bimetal element It. The combustion switch CS is preferably mounted Just outside a combustion chamber CC with an opening ii in the wall of the chamber to permit radiation of combustion heat to the element l0.

As shown in Figure 5, the effect of the heater H on the bimetal element It may be somewhat varied, as by interposing a rheostat R in the room thermostat circuit. We have found in actual practice, however, that the combustion switch is not very critical, and in the usual run of installations the size and amount of resistance wire for the heater H can be readily predetermined.

Our burner control system is adaptable for all high voltage installations, as illustrated in Flgure 8. wherein a room thermostat RT is of the high voltage variety and acts as a main or motor switch for the burner motor BM. The heater H s f course somewhat heavier, to take care of the heavier current flowing through the burner motor and yet secure approximately the same heatdotted position illustrated when the parts are in:

the position of Figure l or when they are in the position of Figure 2. A spring)! is provided to swing the latch 2| into a lock out position, shown by solid lines, whenever the contacts I4 and II areseparated,uinl'igure3orFigurei. The burner system thereafter cannot recycle except after the end 23 of the latch 2| has been pushed upwardly manually for resetting the combustion Puc'rrcu. Ornsrrox Normal operation With the combustion switch in the cold position of-Figure 1'. closure of the room thermostat elects energisstion of the relay coil RC and the heater K through the combustion switch contacts it and" from the secondary B of the transformer T. Iinergisation of the relay coil effects closure of the motor switch M8 whereby the burner motor Bid and the ignition mechanism In of the burner are energised Energization metal element It to be heated and thereby warped, but this is a relatively slow process. Accordingly the bimetal element It does not warp enough to of the. heater H causes the bi- Combustion failure after combustion has been established Referring to Figure i, combustion has been established thus moving the parts of the combustion switch to the position of .Figure 2 and then combustion has failed so that the bimetal element ll begins to bend back toward its original position, due to cooling down of the combustion chamber. Accordingly, the contact it will leave the contact II when the energy built up by straightening of the bimetal element is suf;

ficient to overcome the pull of the magnet ii on] the armature II. The contacts I4 and it thereupon open with snap action. The relay coil is now de-energized, so that the motor switch opens and a purging period will be provided, during which the elements Ill and I2 cool to their initial separate the contact 15 from the contact ll be- I fore combustion chamber temperatures start W rp ng the bimetai element It, so that the contact It follows up the contact II. The magnet ii and the armature ll also aid in keeping the contact. I4 and I I engaged. The bimetal elements II and I! may be placed under some initial tension when mounted on the insulating block I! if it isetdesirable to eliminate the armature and macn Subsequently, when the room thermostat opens, the relay coil is de-energised to thereby open the motor switch and stop the burner. The parts iii position. The contacts I4 and II are thereupon re-engaged to recycle the burner.

The operation of Figure 5 is substantially the same as already described, the rheostat B being provided for the purpose of changing the heating value of the heater H so as to compensate for diflerent conditions encountered in different installations. It is believed obvious how Figure 6 operates in substantially the same manner as Figure l, with the burner motor current passing directly through the mom thermostat and the heater.

The combustion switch we use in our burner control system is a combined combustion switch and safety switch in that the contacts II and I! are separated as a result of a cold combustion chamber CC and a hot heater H. Whenever these two events occur at the same time, then the burner is shut down for a purging period and recycling. As long as the burner operates on normal cycles the contacts I4 and it remain engaged and are never separated. Separation occurs only when there is either an initial combustion" failure or a combustion failure subsequent tocombustion establishment.

In the operation of our combustion switch when constructed in accordance with Figure 7, a flame failure either initially, as in Figure 3, orafter establishment, as in Figure 4, will result in the and I! will then cool down to their initial poeitions, as in Figure l, for another burner operating cycle.

ream o] combustion to be established Referring to Figure 3, if combustion does not occur inv the normal manner, the bimetal-element II will remain in its. cold position while the bimetal element It will move to its hot position, due to energization of the heater H. This will take preferably about a minute or so,a1though the time does not have to be as long as it takes the usual safety switch in a stack switch installation to trip out. The room thermostat circuit is now opened latch 2i assuming its lock out position, thus preventing a recycling of the burner until after the trouble has been remedied by a service man and he has reset the combustion switch.

Our arrangement is such that we have the combustion switch responsive to combustion chamber temperatures from a point exterior of the combustion chamber, where temperatures range only from 70' to 200 Fahn, whereas the temperature responsive element of a stack switch must withstand temperatures inthe neighborhood of 700- Fahr. Our combustion switch entirely eliminates a slip connection and is so designed as to combine a warp type of safety switch with the combustion responsive element. so as to use a single set of contacts instead of the usual arrangement of one set of contacts for the combustion temperature responsive element and another set for the safety switch. The movement of the bimetal elements from the position of Figure 1 to the position of Figure 2, it will be noted, causes the contacts I4 and I! to wipe across each other, thus keeping them clean at all times.

We have found that rather wide variations in combustion chamber temperatures and heater temperatures do not materially affect operation of the combustion switch, and the bimetal elements it and I: are able to keep in step during normal responding, warping in the same direction and maintaining said contacts closed whereby heating of the heating element and a cooling or a cold condition of said combustion chamber eflects separation or said contacts, an armature carried by one oi said bimetalelements, a magnet cooperating therewith and carried by the other bimetal element, said armature and said magnet tending to keep said contacts in engagement and eflecting snap action thereo! toward open position when the energy in said bimetal elements is such as to overcome the pull of the magnet on the armature, and mechanical latch means to hold said contacts out of engagement when they snap to open position.

6. In a burner control system, a burner motor, an operating circuit therefor including a switch, means responsive to room temperature for efl'ecting closure or said switch. a circuit tor the room temperature responsive means having a combustion switch and a. heating element connected serially therein, said combustion switch comprising a pair of bimetal elements, a contact carried by each or said bimetal elements, one of said bimetal elements being responsive to combustion chamber temperatures and the other one being responsive to heat from said heating element, an armature carried by one of said bimetal elements. a magnet cooperating therewith and carried by the other bimetal element to keep said contacts in engagement and eflect snap action thereof toward open position when the energy in said bimetal elements is such as to overcome the pull oi the magnet on the armature, and latch means operable to hold said contacts out of engagement after snap action has occurred, said latch means being releasable to permit said contacts to reengage after said bimetal elements are both cold. JOHN J. RO'I'HWELL. LELAND B. WAGNER. 

